Light projecting system



Oct-:4,f1938. ESBRAeKEfT 2,131,852

` LIGHT PROJECTINGSYSTEM Filed July 2m 1936 5 sheets-sheet 42" n Och-4, 1938. F. s. BRACKETT 2,131,852

LIGHT PROJECTING SYSTEM Filed July 27, 1936 5 Sheets-Sheet 4 LIGHT PROJECTING SSSS EM i UNITE D 'S'TATS Patented oci. 4, 193s PATENT OFFICE This invention relates to improvements inv light projecting systems, including especially -head- C lights; but embodies-principles applicable'in spotli'ghts`,"prolectors andthe like; l i i Ixiessence,`the invention comprises the com bination of a light source, alensiorcombination of lenses) and a reflector designed for, and`com" e plementalto, the'len's (orcombination of lenses). `By the expression designed for, and complemenl@ tai4 to, the lens" Ifmean such an interdependence that,^v'1ith' change in the'character,` or placement,

of the lens a change is necessary in the shape of the renector.Y i

In addition tovthe `-conventional `paraboloid.

` u there are two systems *which have been common in the art;

y il)` Lens. light source and spherical reilector,

lens and at the center of curvature of the `reflec- .n tor. i

; y source,` thus yielding a pattern which is more spreading andsofailsto yieldasconcentrated a patternas maybe desired: hence, the gain over Y the nrst form may toa considerable .extent be The present invention furnishes an improvemeut overbotli fof lthe above systems common to the 'art,in that it minimizes-magnification while it utilizes `a large solid angie -This is accomshape, which-shape is dictated by the spherical aberrationof thelens.` The source is placed at or behind the principal point of the -lens forlits axial zone. Due to sphericalaberration,` each zone of thel lens as one progressesoutwardly has "its principal; point ycloser4 and closer to the lens.

In ordenthat the zonal. portion `of the reflector which; supplies the radiationto each corresponding z'onexof thelens `direct the radiation to the m properpointfor parallel emergent rays, the ra- (i.` e.,,to produce parallel light or light convergent.

diusof curvature must increase and the center t of curvature moveiorward towardthe lens as one considers,l zones of progressively greaterY di-` ameters For a given lens used in s.` specified `way flector, are specified. the source lying at a principal focal point of the plishedbyjthe construction of a reflector of `novel t to a specied point) the proper shape of reflector is uniquely determined.` -Where "spherical sur-- faced lensesv of large diameter (for the 1focal length) are used, the resulting reflector differs greatly from the conventional spherical form.

Furthermore,` several times the solid', angle is utilized.' Y i i In essence, therefore, my inventionprovides a' means `offsecuring in a practical way a' greater concentration ofenergy by turning to advantage the spherical aberration ofthe lens.` Y

It is obvious that the same can be done to advantage in systemsof more than one lens. The reflector is then uniquely determined as to shape when the characteristics Yoi thelenses and their placement, and the placements ofi lamp and re- It should be noted that a wnole classe` of lenses and lens combinations.` because of similarity in spherical aberration, may require an identical mirror form. Furthermore, in a lens-system the separation may be adjusted so as to use a particular mirror.

` The various embodiments hereinafter provided pertain to particular functional demands as to pattern, etc. For simplicity the term refractor will be used to indicate a single lens or a combination of lensesf The term spherical surfaced lens will be used inthe broad sense to mean a refractory material bounded by portions ofspherical or plane surfacesfat least one surface being sphericah f Embodiments of the invention will be described withgreater particularity in the following,`taken in conjunction with the appended drawings, in which e Fig. "1 is a diagrammatic view illustrating the optical system of the invention in a simple form thereon' i Fig. 2 is a view similar t o Fig. ibut illustrating a modification in which an additional reflecting surface is employed;

Fig. 3 is a diagrammatic view illustrating a `modincation of the optical system shown rin .F1

s. 1: Fig. 4 illustrates a further modification of the inventionin which the reflector lis modified anda lens system is employed; t

Fig. 5 illustrates an embodiment of the invention in a headlight;` I

. Fig. 6 is a detail view of the member fwhich provides an additional reflecting surface; j

`Figs. and 8 illustrate modifications of the spherical reflector shown in Figs. 23 and 5, `and Fig. 9 illustrates a further modification of the optical system of the invention.

Fig. 1, which illustrates a simple embodiment of the invention, shows the combination of a single lens L and light source Fi with co-operating reflector M designed in accordance with the principles of the invention. The lamp Fi is placed at the principal focus of the central zone of the lens L, or behind it. Lens L may be any type of spherical surfaced lens, preferably a plano-convex lens as shown. The portion a, a, a of the reflector M is so formed as to direct rays in a parallel beam from the lens by compensation of spherical aberration of' the latter. Thus, the surface of the reflector in the axial zone thereof, reflects the rays to the principal focus of the centrai zone of the lens. As one proceeds away from the axis, the reflector M is made up of zonal elements whose foci are progressively farther and farther in front of the filament (towards the lens L), so that for all zones a, a. a of the reflector M the rays pass through the proper focus for the zone of the lens L illuminated by that portion of the reflector. For instance, in Fig. l, rays 2, 3, 4 and 5 are so directed that they emerge parallel from the lens L, or substantially parallel.

The resulting form of reflector M is neither spherical nor ellipsoidal but a novel form determined by the spherical aberration of the lens. Such a surface is complemental to the lens, or lens system, for which it is designed.

Referring to Fig. 1, where in addition to a high central illumination (such as is illustrated by the rays shown in ,solid lines), one wishes av widely spreading pattern, the reflector surfaceV may be extended in the following manner:

The segmental portion a, b, c of reflector Mis so formed that it constitutes a portion of an ellipse, one focus Fi of which is at the filament and the other focus F2 is near the edge of the lens (or lens system), or in front of the same as shown, so that the rays reflected thereby will pass through the lens in the opposite half, and preferably near the edge, of the lens. The surface of the reflector would then be generated by rotation about the axis of ythe system; i. e., one focus of the elliptical segment describes a circle during generation of the system. Thus the surface generated is not an ellipsoidalthough it is swept by a portion of an ellipse.

In the showing made in-Fig. 1, the rays shown in solid lines represent the portion of the total light (passing lens L) reflected by the comple-4 mental portion of reflector M: the rays shown in broken lines represent direct rays, While those shown in dot-and-dash lines represent rays reliected by the segmental portion a, b, c of reflector M. Accordingly, it will be observed that a substantial amount of the total illumination passing lens L lies below the axis of the system and is disposed in a spreading pattern.

It will be understood that the reflector M may be made a complete figure of axial symmetry. where one desiresa symmetrically spreading pattern.

If one wishes a unilateral pattern one may introduce suitable diaphragms which cut off upwardly directed rays. Such obstructed radiation may, however, be recovered by the introduction of a mirror, spherical in form, such as the mirror S of Fig. 2, kwith the center thereof at the filament or near it. Thus, a spherical mirror may be so chosen that it serves to obstruct any rays that otherwise emerge upwardly, and" direct them so as to reinforce the central and lower portions of the useful pattern. With use of the spherical mirror a diaphragm, as such, may be dispensed with. The spherical mirror S illustrated in Fig. 2 obstructs all direct radiation which would otherwise emerge upwardly. Its center is at the filament F1. It reflects all radiation" outside the region of the complemental surface a, a. a so that it will emerge from the lens in the downwardlyor downwardlv and laterally-disposed direction.

The spherical mirror may be substituted for any portion of the complemental surface, in the lower half of the latter, thereby reducing the intensity of the central pattern and increasing the intensity. ofl the more widely spreading portions of the pattern.

'I'he forward or limiting edge of the spherical mirror S functions as a diaphragm. By varying the distance between the limiting edge ofmirror S and the filament different degrees of sharpness in the cut-ofi of the pattern may be secured. y

Figure 3 further illustrates the configuration described above with reference to Fig. 1, of a reflector M which is complemental to an arbitrarily chosen plano-convex lens L. A method of arriving at the proper configuration of reflector M in this simple combination lens-reflector light source follows:

For parallel light lens characterized by zonal foci f1, f2, fa, f4, fs as a result of spherical aberration:

Arbitrary choices 1. Distance Sh (limiting case S at fi) 2. Distance Sao (practical lowerl limit set by size of bulb) Shape of reflector is uniquely determined by the demand that rays from S be directed by refiection to points f1, f2, fs. f4, f5 as indicated.

Construction of reflector is as follows:

1. Zonal foci fl-fs are determined so that accurate drawing can be made showing rays projected backward from lens.

2. Curve of reflector is developed graphically in drawing starting at ao and extending element by element so that each element of surface is so oriented that its tangent makes equal angles with rays fr a1 and Sai, ,f2 a2 and Saz, fa aa'and Saz, etc., to a5, successively.

3. A templet is then cut in accordance with the drawing from thick flat metal stock with. its inwardly disposed edge polished.

4. The templet is then mounted in proper relation to the lens so that its inward edge acts in place of a portion of the mirror, a mask is placed over the lens covering .all but part i-5.

5. This testarrangement is then directed toward adistant source of light (such as thesun) and the interrelation of the rays at or near S is examined. The reflecting edge of the templet is then corrected by trial and error until the aforesaid critical interrelation of the rays at S is obtained. l

The mold from which the reflector is to be spun or stamped in the conventional way is then turned in accordance with the templet.

It will be seen that the greater the focal length of the complemental surface the smaller will be the solid angle of radiation directed by the complemental surface into the parallel beam emergent, and consequently the greater the solid angle of radiation which can be directed into the more widely spreading portions of the pattern. Thus the degree of concentration ofintensity within the pattern can be controlled both by selection of focal length and by the amount of 11ers intenseuat tneedge.

` placeof fthe"complementalsurface. Y. V; y Thezradius of` curvature of the spherical"vmir-o` o, Lror is Iso chosen that? its jforward land upward :Sledge may befxnoreor less sharply defined in the -pattern, thus yielding a harderor softer boundary tionsof thepattern.`

i system,- while rayslstriking the non-complemental tportionyof .the reilector emergeln a downward more and more widely: the "result is asmoothly igra'ded pattern more intense: at the L center and .Fig. 4'shows1a projectorsystem comprising a `objective lens O, ileld lens Fgretlector Maand'a lament Fi. The illamentuislocated `atfor Just e o behind, the principal *focus voi.` the? central zone :of the lens system' F310. #Lens F is `so `vchosenasto direct radiation `(excepting-that'lost dueto irn- `ffllamentpassesv through the lens O: is so `located with respect to lens O that `it lies near,

. tions ofllensO.l

The mirrorMA i's complemental in the region flected Iby. the complemental surface emerges vface Mr is'extendedfrom" the complemental suro face, merging smoothlyiinto@ a cone `e-`c, the aggregon cal--ca` beingy a transition region between "l the complementar ace and `the conical sur- Radiatmnfrenected fromme conical para@ `cl'c` is directed by the mirror M4 as from a focus `FYI-which lattersweeps `a circle as onepasses to straight line l The radius of curvature of the' ileldlensrF is -emergesfrom the ileld 1lensin a divergentcone `whereasthe` reiiected rays from F1 emergefrom "the ileld lens parallel to Vthemselves or"`co`nyerging l but also" still lie within o thel domainj or the ob.,

" `lective in. the opposite hali.lv The radius fof .o limiting ray `from the periphery of the iield lens forming apart of the bundlefrom F1 escapes the symmetricalsystem'` substantially the whole `solid angle ofradiation is projected in a symmetrical i pattern intense `lin the center with a Iwideiield l i 1(6O,to 70) of gf `eralillum`ination evenly gradfed"` fromthel center and weakat the border. `Attention is drawn, inthisconnectiomto the factltliatl the functlo'n'zofl the loonical surface `c l plus fleldlen's `F isVeq'uivalent `to the1 function .1; of the surface inthe embodiment shown in" Fig. f 1 generated by the ellipsefonefocusv of `whichis oiiaxis.k

ical fmirrorf S w mayF be substitutedtfor any portion of the mirror M4 in one hemisphere.'` If gy; l the `regionale-a and cc` in onefhemisphere are `'"5 eliminated, a semicircular pattern is produced.

` between thelilluminated andiinillulninated` por-V f Referring agamto rigxoaftheuppefmost ray. o 3. strlkinglthecomplemental portion of the reflector,l

u emergesrfromlthe lens "parallel-to the axisfof` the spherical mirror Suis Vquadrant. i l .Y o

'Ihe base of the light bulb,` creating an uniavoidable, obstruction to radiation,` `may be dis-l i posed in such a1 manner -asitofobstrct radiation `and laterally spreading direction.` Successive 1` which otherwise would `contribute toaluseless rays, as oriermovesl away from the fooniplernental surface,contribute illumination which spreadsl venience indicates.

diameter and curvature that substantiallyjall Arlperiect transmission and reflection) from the` but in` frontof, the principal focus of all por` parallel `from the Ilens system. The mirror jsuro different portionsfor thesurface swept outby the such that the ydlrectradlation from the illament `falling within the aperture of the objective O,

llens F at `alifanglejust:less` than 90,` thus avoiding total internaliretlectiont In a complete `axially `If `an-unsymxrretrical pattern is desired a spher-` Ifjless' central intenslty'is desired, the lower lhalf 'of the .complemental mirror maybe tunitted'A and c u an' `extension of spherical "mirror S 'substituted therefor; thus .increasing the intensity of.; the outer portions of@ the pattern and reducing the intensity ofthe central portion.` i.

1 "If a three-quarter quadrant `pattern is desired. `f-mirror-Mr is disposed inthree quadrants and restricted to the` fourth,

portion 'ofthe `pattern unlessreiiected by-a porthe bulb, socket and spherical mirror "tofbe @mounted as` a unit. whichunit can` 'be removed for `re-loadingl-through an` opening in the lower jury; furthermore, `it enables the "manufacturer permanentlyto seal th'e system as avwhole, only n asmall' opening ever belng`- exposed,which opening `can be i completelyj sealed upon replacement of the bulb` and mlrror`unit,it beingpossible `to pr'ovide a suitable dustiilter in the casing to `permit "location of thisbas'e is downward: it`v` nriaybe tiltedvbackwardly or towardsthe front as con- Thisy arrangement permits Jil Vportion of the casinglfof"theicomplete system. This-has the advantage ofleaving the main optical system undisturbed andfprotectedfrom in- '2.3

breathing without the introduction of" dust. i

Thus, the otherwise substantially air-"tightcas-` ing may be pircedto provide an opening to 1e ceive therein a replaceable air-filtering -unlt such for instance asa shell containing suitable alr- Y `filtering medium (e.`-g.`,1`cotton` wedding,` glass -wool, silk waste. or the like) through the medium of whichshell air pressure within the casing may .l readily beequalized lwith that ofthe surrounding atmosphere.' Such an arrangement Ifunctions'to exclude'dust from wlthinthe casing and ythus prolong the period ofhlghefflciency ofthe fdqvlce. l l1?" v Similarsystemscomprising objective, field lens, reflectors and light source may be constructed `.of `different sizes. n n sai-ily, because of manufacturing limitations, the greater are the `focalflengthsfandconsequently' The larger` the Alenses `necestheless is the magnification, the more "concen trated the pattern and the less `the field-angle. Thus theembodiment-showninlFig; 5 yields from 10 to 20F less field-and a'ismaller and more in- 1 tense central 'spotfthan "does the construction InFig. 5 I represents a sotrearnlinedmetal shell ora headlight in the base of which'a solid'fblock Y 2 ofl suitable `metalisrigidly'secured, aportion of the shell' l being cut `away to forman open-Iv ing in thelatter exposing a part offth Vbottom'surface of block 2. 4 represents laxthreaded bore inblockr! `for the reception' of 4aiclamping bolt (notshown) 'for fliringthe headlight on Va su'table supporting part of ma vehicle. 'o A washer` i 5, having a cup-shapedV outer` face 6, is positioned `-i'n opening 3. 3 abutting block'Z; a suitable (e. g., rubber) gasket 1 may separate inner surfaces of Vwasher from outer surfacesof shell l."

An annular sleeve 8, 8 is secured, at its inner,

` outwardly flanged end 9, 9, to the inner' surface ,of shell l, extending outwardly to a point just within the circular opening I0, Ill inthe `front of shell l, wherewit terminates at the ln`turned v end `ll,`i`l. Asecond sleeve: l2, l2, concentric with 8, 8, `andhaving inner outwardly-daring end flanges. I3, I3, is removably fixed to sleeve 3, 3: it extends Ithrough opening I5. I0, in shell Inside shell I and to the rear of lens lIl there is provided an annular supporting sleeve I3. I3. the same being secured in position by suitable attachment to sleeve ,3. 3 at a plurality of points therealong. one such attachment being shown at I3. Sleeve I3 may, as-shown. be made slightly tapering inwardly. Its rear end 23, 25l is bent inwardly and then backwardly, i. e.. toward the lens I5,'and inwardly, to present an annular retaining groove 2I,2I for the reception of a planospherical lens 22 the periphery of which is pressed by gasket 23 against an annular ring 24 secured to the in-tumed end 25 of supporting sleeve I3. A reflector 25, having a 'polished inside surface. is secured to supporting sleeve I3 by means of a pluralityof bolts 25 passing through the inturned end 25. annular ring 24,-a resilient gasket 21 andthe outwardly daring periphery of reflector 25. A circular light filter 23 is mounted between annular ring l24 and gasket 21, and a diaphragm 231s mounted between gasket 21 and the periphery or reflector 25.

V Reflector 25 is a cup" which in the portion c thereof adjacent support I3. is conical in form, merging smoothly into a shape a, "a", complementa] to the lens .system at the bottom (or rear), the complemental surface having been developed from an almost infinite number of zonal elements complemental to the corresponding zones of the lens system whereby to effect parallel emergence of the rays'reected thereby.V

Point 30 schematically represents the center of the filament of bulb 3| which filament center is on the longitudinal axis of'the shell I and of the lenses I6 and 22 and reflector 25. and is located at. or Just behind, the principal focus of the central zone of the lens system I5, 22. Lens 22 is so chosen'aseto diameter and curvature as to cause'all direct radiation from filament "to pass through lens I5, and'is positioned with respect to lens I5 so as to be near, but in iront of. the principal focus of all portions of the latter. The upper portion of diaphragm 20 is bent rearwardly. and its upper edge lies close to but slightly belowthehorizontal axis of the system.

Shell I has an opening 3,2, 32in its base immediately to the rear of block 2which opening normally is closed by block 33; Block 33. whose lower surface conforms to the surface of shell I, has ball-shaped upper surfaces 34, 35.' A portion of the rear wall of .block 2 is shaped as a socket 35 complementa] to ball-surface 34 of block 33, the top of the rear portion of block 2 being cut away. Block 33 carries a rearwardly-directed projection 31 which engages the top of thethickened shell portion 33', which thickened shell portion has a socket-shapedzend surface complemental to ball-shaped surface 35 of block 33. 39 represents a depression in the lower surface of block 33 for the receptionof a threaded bolt 45 which passes through an opening 4I in block 33 and threadsinto threaded bore 42 provided in block 2. f Y

Block 33A supports the bulb 3I. sleeve 43 of the bulb means 44, 45, 45,

the socket for adjust- A53, which tightly nts the upper endof sleeve distesa ing the direction of sleeve 43 and a spherical mirror 41 carried on socket sleeve 43: accordingly, elements 3|, 33. 43 and 41 may befremoved from shell I as a unit (for' replacement of bulb 3I or'adiustment of the angle of sleeve 43) 'by removing bolt 40, forwardly pivoting the unit base 33 through resilient sleeve 43. Intermediate the ends ofsleeve 43 there is secured about the latter an annular flanged collar 44 provided with a plurality of openings 50, 50 through which bolts 45, 45 loosely pass. Bolts 45, 45 are threaded into block 33. A plurality of compression springs 45, 46, through which bolts 45, 45 pass. tend to press i'langes 44, 44 away from base 33, against which pressure-adjustment of the yangularity of sleeve 4 3 may -be had by suitable adjustment of bolts 45,. 45.

Sleeve 43 is provided, near its upperend, with a bayonet slot 5I for engaging andholding the pin 52 of bulb 3|. f

Sphericalmirror "terminates in a sleeve 53, 43

and which'is flxedly mounted on th'e latter. It

`is so positioned on sleeve 43 that the peripheryI of spherical mirror 41 lies close to but below the horizontal axis of the system. A portion of the mirror 41 is cut away to provide a semi-circular opening 54 at the rear of the mirror, whereby to permit a lportion of the downwardly and rearwardly directed radiation from filament 30 to strike upon and be reflected by the contraspherical, surface a, a, a of reflector 25.

A portion of reflector 25 lying outside the field of direct illumination by filament 30 is cut away to provide an opening 55, 55 through which sleeve 43. spherical mirror 41 and bulb 3I may be passed as a unit into and outof the interior of reflector It will Abe understood that other` angularityadjusting means than that specifically shown inA f Fig. 5 may be employed: also, that filter 23 may be used or omitted as desired, and that both surfaces of the filter-23 maybe plane orone surface plane while the other carries vertical corrugations. v

Moreover, the invention is not restricted to the use of lenses whose surfaces are rigidly spherical or planerone may superimpose on at least a portion of such generally spherical (or plane) surface a suitable corrugation to increase the lateral spreading or to modify the distribution of intensity in the pattern. This .is illustrated in Fig. 4 wherein corrugations have been superimposed on the rear, (plane) surface oi' objective lens 0.

In conjunction with any of the systems above v described a color filterv may be introduced to modify the color4 of the projected radiation. This is illustrated in Flg. 5. Where the filter is placed near the objective lens, a'suitabie corrugation may-be superimposed on one surface of the illter,thus producing a desired spreading of the illumination, as this may be found to be more convenient, from a constructural standpoint, than superimposingthe corrugations on the lens. 0r, corrugations may be impressed on a clear glass disc,.and such corrugated disc positioned in operating relation with the lens or lens system, in lieu of a filter.

Ii' a three-quadrant is desired, a portion of the 1` spherical mirror may be a vertical dividing plane, V `opposite to that quadrantY ofthe pattern which is.`

vto, `be illuminated. In suchcase, A i the `elliptical generation of `the `reflector is extendedintothequadrantwhere the spherical mir- `This is illustrated in Fig.

` y ror has been cut away.

. `been eliminated. When cutaway on oneside of the. side cut away being the surface of '7, in which one-half f` the spherical mirror has I desire illumination in the upper right quadrant of the pattern I cut away one-half, or slightly lessthan one-half, of

the spherical mirror in a vertical plane approxin mately through the" axis of the system.

i Fig. 8, cutaway a left-hand, iront, `portion of the y l through which a i lower quadrant ofthe Where a less intense upper right quadrant illumination is `desired I may, as is illustrated in spherical mirror whereby to yield an` opening `Q direct illumination of the left spherical aberration `of the lens` or lenses, the

rays are directed in a spreading manner to the f right upperpquadrant of the pattern.

tance. In this embodiment In Fig. 9 is shown a combination of a lens sys-` tem Li, La with alight source F1 and the above described complemental reflector M, wherein a point, orspot, focus is desired at a specified` disthe emergent rays from the lens systemarezconvergent to a point.

If one wishes to .prevent illumination outside ofa small spot, a diaphragm D may be inserted i at the circle of least confusiomthegdiaphragm suitablev aperture will serve to prevent rays which useful beam.

preventing direct radiation from the filament from` illuminating" the lens system where, `due to` i y `spherical aberration, `undesired spreading.

suchradiation would create A spherical mirror `S may be so disposed that its axial zone will occur inthe plane l),A so that a otherwise would spread the `pattern from reaching the lens system: said spherical mirror S reinforces the illumination of` thel complemental re fiector in` such `a `manner that `the raysemerge' through the aperture A, thus contributing tothe Whereafringed pattern is desired, the aperture may be made larger, `thus permitting, a full, direct illumination'of the lens system by` the filament. Ii. a more bodiments above discussed.` y An importantfeature ofthe `invention is, as

has been suggested `hereinbefore, the provision of a` substantially `tight headiight,or spotlight, or

other light projector, casing in which is located means for equalizing pressures interiorly and vexil `teriorly f of the casing.

Byl `this modification I am enabled to `prolong the useful life of the apparatus and greatly to retardthe `necessity for cleaning or polishing the cation is illustrated in Fig. 5 of the drawings, wherein is shownV a breather" element, in the form" of a cartridge, fixed (e.` g., removably fixed, as by screw threads) in an opening 61, 51,

. ment may lens is` effected. Due to spreading pattern is desired, the reflector may be extended beyond the complemental area in` a manner similar to that in em i of which is oir axis by a. portion at the source ofillumination and the other focus to such an extent that subradiation reflected by `said ward radiation through a real focus nearsaid source to said elthe first-named reflector. fThis modifispect to each fibrous, or equivalent, filtering material such, for instance, as like. The cartridge may take any one of a number` of forms, it being essential only that the vcartridge have air-permeable openings at either end .and that its filling be capable of abstracting Vportion of which is composed of segmental zones each of which is so developed as to send its reglass wool, cottonwadding, or the,`

in the casing, the cartridge1 containing a mass of dust, `from air entering the I fiected rays to a selected and consecutive portion f of the lens,vthe curvature ofy each segmental zone being so configurated as tocompensate forspherical aberration of thecorresponding portion of the lens, said axial portion merging into a` por-` tion which is generated through revolution about the axis of the system by a portion of an ellipse one focus oi?` which is `at the source of illumination and the other focus of `which is oil? axis to such an extent that substantially all of the radiation reflectedv b'y said portion generated by the ellipse passes through the opposite half of the lens, said source of illumination, lens and rel flector being so disposed other that rays intercepted by said vaxial portionv of the` reflector emerge from said lens essentially parallel to each other.

Y 2. An optical `systemv comprising in combina- 1 tion a source of illumination, `surfaces is plane and is convex and spherical, a concave'reilector the a lens one of whose the other of whose surfaces axial portion of whic is composed of segmental zones each of which is so developed asto send with respect to each,`

its reflected rays to-a selected and consecutive l portion of the lens, the curvature of each segmental `zone being so congurated as to comv pensate forspherical aberration of the correspending. portion ofthe lens, said axial portion merging into a portion which is` generated through revolution about the axis of the system of an ellipse one focus of which is stantially `all of the portion generated b ftheellipse passes through the `oppositefhalf of the lens, and a substantially spherical mirrorso disposed` as to return downfrom the source of illumination liptically generated portion* of reector, saidsource of illumination, `lens `and `first-named reflector being so disposed with reaxialportion of said rst-named reiiector emerge from the lens assentially parallel to each other. FREDERICK S. BRACKE'I'I'.

other that rays intercepted by saidy 

